Superheterodyne receiver



y 1936 w. J. OBRIEN 2,039,923

S UPERHETERODYNE RECEIVER Fil'ed Dec. 4, 1954 INVENTCR' W. J. O/ IZ/Z-W BY m g ATTORNEY Patented May 5, 1936 UNITED STATES PATENT OFFICE SUPERHETERODYNE RECEIVER Delaware Application December 4, 1934, Serial No. 755,872

8 Claims.

It is an object of this invention to provide a superheterodyne receiver in which automatic tuning to the desired station is effected.

A further object of the invention is to provide a novel form of superheterodyne receiver in which the oscillator portion of the set oscillates only when a desired station is being received, undesired stations causing no signal to be passed through the intermediate frequency amplifier and sound reproducer.

A still further object of the invention is to provide in a superheterodyne receiver a separate exciter tube having a plurality of grids with means for impressing the intermediate frequency on one of the grids and means for impressing the oscillations generated by the exciter tube on a grid of the first detector or frequency converter tube.

Other objects of the invention will become apparent to those skilled in the art as the description thereof proceeds. The novel features which Iv believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method ofv operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically a circuit arrangement whereby my invention may be carried into effect; In the drawing 34, 35,36, 31, and 38 denote electron discharge or vacuum tubes having the usual cathodes l3, control grids l4, screen grids l5 and plates I5, four of the grids I5 being connected to a source of positive potential +3 and all the plates being connected to a source of steady plate voltage +B. Tubes 34 and 38 are shown as having an additional grid electrode I! located adjacent their cathodes. The source of cathode heating potential has been omitted in each case for clearness, any such source well known to those skilled in the art being suitable.

The input circuit of tube 34 comprises a radio frequency transformer having its primary Winding Ill in the antenna circuit and its secondary ll tunable to the incoming signal frequency by a variable condenser l2, and being connected to grid M. The plate I6 is connected to the intermediate frequency transformer comprising primary and secondary windings 21, 28 each of which is eX- actly tunable to the desired intermediate frequency by an adjustable condenser 29. The intermediate frequency currents are amplified by tube 35 whose plate circuit is connected to the control grid of second detector 36 by the sharply selective circuits comprising primary 21, secondary 28 which are sharply tuned by condensers 29 to the same intermediate frequency. Any known arrangement may be used for detection in connection with tube 36, in the arrangement shown the tube operating as a power detector the control grid being given the proper negative bias by the battery 33. The audio frequency currents in the plate circuit of 36 may be amplified in an audio frequency amplifier 3! this tube being shown as coupled by a transformer 30. The amplified current in the plate circuit of tube 3'! may be impressed on any desired type of sound reproducer such as the loud speaker 32 coupled to the plate circuit as by a transformer 3|.

Connected between the grid ll of the frequency converter or first detector tube 34 and its cathode is a circuit comprising the transformer secondary coil 24 shunted by a variable condenser 25, the primary 23 of the transformer being connected in series in the plate circuit of exciter tube 38. I term this an exciter tube since it causes oscillations of the proper frequency to be set up in circuit 2425, in the absence of the usual feedback connections between its plate and grid circuits. The signal control grids [4 of tubes 34 and 38 are connected by a lead 33 and the grid ll of tube 38 is connected to grid M of intermediate frequency amplifier tube 35 by a lead 22. Means are provided for controlling the transconductance of tube 38 such as by connecting its screen grid to a sliding contact I!) adjustable along the resistor 20 to one end of which the positive terminal of a battery 2| or other voltage source may be connected. The control grids I4 of tubes 34, 35, 31, and 38 may be given the proper negative bias voltages as by the self bias resistors l8 or equivalent means. The rotor plates of condensers l2 and 25 are preferably mounted on a common control shaft, as indicated by the dotted line 26, the shaft being rotated by a control knob as diagrammatically shown.

It will be understood that the condenser I2 is adjustable to tune the signal grid circuit of tube 34 to the incoming modulated signal frequency this frequency being, for example, any frequency within the broadcasting band. It will also be understood that condenser 25 is adjustable to tune coil 24 to a frequency which differs from the incoming signal frequency by an amount equal to the intermediate frequency to which coils 21 and 28are resonant, the oscillation circuit 24, 25 being preferably tuned to a frequency higher than the incoming signal frequency. It will be understood that the circuits 21, 28 and 29 have a much lower ratio of reactance to resistance than the resonant circuits ll, l2 and 24, 25 so that they are much more selective as to frequency.

In the operation of the device, the condenser I Z is adjusted to tune the input circuit to a desired signal frequency, for example 1,000,000 cycles. This frequency is also impressed on grid [4 of eX- citer tube 38. Assuming that the circuits comprising coils 21 and 28 have been adjusted to a resonant intermediate frequency of 100,000 cycles, it will be seen that this frequency is applied to grid ll of tube 38 so that the plate current of this tube will vary at a frequency equal to the sum of the signal frequency (1,000,000) and the intermediate frequency (100,000). Condenser 25 has been so adjusted as to make circuit 24-45 resonant to 1,100,000 cycles, the frequency of the current passing through coil 23 which is inductively coupled to coil 24. As one end of coil 24 is connected to grid ll of the first detector, the desired difference frequency between 1,100,000 and 1,000,000 will appear in the plate circuit thereof and after amplification and detection in tube 36, its modulation component will operate the loud speaker. Under the conditions described it is seen that the exciter causes circuit 2425 to oscillate at the proper frequency to produce the desired intermediate frequency in the plate circuit of the tube 34.

With condensers l2 and 25 at the same setting, consider an incoming signal frequency of 990,000 cycles. This would; produce a frequency variation of 990,000 cycles in coil 23 but as coil 24 is resonant to 1,100,000 cycles, the circuit comprisingcoil 24 and condenser 25 will not oscillate so that no local oscillation frequency will be applied togrid l1 and no intermediate frequency will pass through circuits 21, 28 and consequently no sound will be produced in the loudspeaker.

With condensers l2 and 25 still at the same setting, consider an incoming signal frequency very near to the resonant frequency (1,000,000) of coil II and condenser l2, say a frequency of 999,000 cycles. Thisfrequency will produce substantial voltage variations on grids l4 and a current of 999,000+100,000 cycles or 1,099,000 cycles will pass through coil 23. This frequency is so close to the resonant frequency (1,100,000) to which coil 24 is tuned, that the circuit including coil 24 and condenser 25 will be forced into oscillation at a frequency of 1,099,000 cycles, thereby supplying an oscillation frequency to the grid of the first detector of the proper value to combine with the signal frequency (999,000) to produce the proper intermediate beat frequency equal to their difference, or 100,000 cycles. From' the above example, it will be seen that when condenser I 2 is set to make coil ll resonant to a frequency greatly different from the incoming signal frequency, no local oscillation frequency is produced and substantially no intermediate frequency currents pass through transformer 21, 2B. As condenser I2 is adjusted towards the position at which its circuit is resonant to the signal frequency, when this position has been closely approached, a local oscillation frequency will be produced in circuit 24-25. of the proper value to produce an intermediate frequency of the value to which the intermediate frequency circuits are tuned and the receiver will function to reproduce the signal modulations.

While specific frequencies have been considered in explaining the operation of the device, it will; be understood that they are illustrative only and are in no wise to be construed as limiting the scope of my invention. I have found that the narrow band of frequencies within which oscillation will commence when the proper tuning position of the dial of condenser I2 is approached may be adjusted in width by adjusting contact l9 along resistor 20 to change the transconductance of exciter tube 38. The band width within which the oscillations commence is increased by an increase of the screen grid voltage.

Having described my invention what I claim as new and desire to secure by Letters Patent is:

1. In a superheterodyne receiver, the combination of a frequency converter tube and an exciter tube, each of said tubes having a cathode, a plurality of control grids and a plate, an input circuit resonant to the signal frequency connected between a control grid and cathode of said converter tube, an output circuit resonant to an intermediate frequency connected to the plate of said converter tube, means coupling said last named circuit to a control grid of said exciter tube, means coupling said input circuit to a second control grid'of said exciter tube, an output circuit connected to the plate of said exciter tube, and means for impressing the voltage variations in said last named circuit on a second control grid of said converter tube.

7 2. In a superheterodyne receiver, the combination of a first detector tube and an exciter tube, each of said tubes having a cathode, a plate and a plurality of control grids, means for impressing incoming signal currents on control grids of each of said tubes, a filter circuit tunable to an intermediate beat frequency connected to the plate of said detector tube, means coupling said filter circuit to a second control grid of said exciter tube, a circuit tunableto a, frequency equal to the sum. of the signal and intermediate frequencies connected to a second control grid of said detector tube, a circuit connected to the plate of said exciter tube and coupled to said last named circuit and means for detecting necting said cathode and grid and having means to tune it to a desired signal frequency, a circuit 1 connected to said plate and tuned to a predetermined intermediate beat frequency, an exciter tube having a cathode and plate, means for controlling the electron flow between the cathode and plate ofsaid exciter tube in accordance with said intermediate beat frequency, means for controlling the electron flow between the cathode and plate of said detector tube in accordance with the plate. voltage variations of said exciter tube, and means whereby the plate voltage of said exciter tube varies at a frequency equal to the sum of the signal frequency and said predetermined beat frequency.

5. In combination in a superheterodyne receiver, a first detector tube and an exciter tube, each having a cathode, a plurality of grids and a plate, a circuit comprising a coil and an adjustable condenser tunable to an incoming signal frequency connecting the cathode and control grid of said detector, a conductive connection between the high potential end of said coil and a control grid of said exciter tube, a transformer primary coil tuned to an intermediate frequency connected to the plate of said detector, a secondary coil coupled to said primary coil and tuned to the same intermediate frequency, a connection between the high potential end of said secondary coil and a second control grid of said exciter tube, a circuit tunable to the sum of the signal and intermediate frequencies connected to a second control grid of said detector tube and means for impressing voltage variations on said last named circuit corresponding to the variations in plate potential of said exciter tube.

6. In combination in a superheterodyne receiver, a detector tube having a cathode, a control grid and a plate, an input circuit connecting said cathode and grid and tunable to a desired signal frequency, a circuit coupled to said plate and tuned to a predetermined beat frequency, an exciter tube having a cathode, control grid and plate, means for controlling the electron fiow between the cathode and plate of said exciter tube in accordance with said beat frequency, means for causing the control grid voltage of said exciter tube. to vary at the signal frequency, and means for controlling the electron flow between the cathode and plate of said detector tube in accordance with the plate voltage variations of said exciter tube.

'7. In combination in a superheterodyne receiver, a first detector tube having a cathode, a control grid and a plate, an input circuit connecting said cathode and grid and tunable to a desired signal frequency, a circuit coupled to said plate and tuned to a predetermined beat frequency, an exciter 'tube having a cathode, control grid and plate, a direct connection between the control grids of said tubes, and means for controlling the electron flow between the oathode and plate of said detector tube in accordance with the plate voltage variations of said exciter tube.

8. In combination in a superheterodyne receiver, a detector tube having a cathode, a plate, a first grid, a second grid and a screen grid positioned between said grids, means for impressing incoming signal voltage variations on said first grid, a circuit coupled to said plate and tunable to an intermediate beat frequency, an exciter tube having a cathode, a control grid and a plate, means for impressing the signal voltage variations on said exciter control grid, means for controlling the electron flow between the cathode and plate of said exciter tube in accordance with said beat frequency and means coupled to the plate of said exciter tube and to the second grid of said detector tube.

WILLIAM J. OBRIEN.

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